Leafroller insecticide resistance management strategy

Lightbrown apple moth
Epiphyas postivittana
populations in Nelson
have developed resistance
to organophosphate and
carbamate insecticides.

P. Lo
Plant & Food Research, Havelock North, New Zealand

(Revised October 2004)

Reasons for strategy and update

Leafrollers (Lepidoptera: Tortricidae) have become resistant to some insecticides in several parts of New Zealand. It is always better to prevent resistance from developing than to deal with resistance once it has occurred. The cost of leafroller resistance to New Zealand could be very significant, and this strategy is designed to reduce selection pressure for resistance as far as possible without jeopardising the quality of produce or export of fruit and other crops. Management strategies aimed at reducing or preventing resistance will help prevent resistance from developing and conserve existing products for ongoing use. This is an update of the earlier resistance management strategy (Suckling 1996).

Background

Six species of leafrollers (Table 1) are primary pests in New Zealand. The caterpillars of leafrollers species feed on a wide range of plants, in addition to those grown as crops. On orchards and other horticultural properties these plants include shelter species, weeds along crop margins and understory weeds, while outside the orchard or crop many ornamental, scrub and native plants are hosts.

Leafrollers are pests of a wide range of horticultural crops, and are generally effectively controlled by insecticides. The extensive and regular use of insecticides in New Zealand horticulture means that the potential exists for leafrollers to develop resistance. However, only a few products meet the crop residue tolerances in overseas markets, and this situation is not likely to change in the near future. This increases the risk of resistance and consequent potential economic impact.

Overseas, several leafroller species have developed resistance or crossresistance to organochlorine, carbamate, organophosphate (OP) and insect growth regulator (IGR) insecticides.

**Table 1:** Horticultural pest leafroller species in New Zealand and their resistance status.
Common name	Species	Distribution in New Zealand	Resistance status¹
Lightbrown apple moth	Epiphyas postivittana	Throughout	Nelson: resistant to OP, crossresistant to C
Greenheaded leafroller	Planotortrix exessana	Throughout	No known resistance
	P. octo	Throughout	Central Otago: resistant to OP, cross-resistant to C & IGR-EA Hawke's Bay: resistant to OP, cross-resistant to IGR-EA
Brownheaded leafroller	Ctenopseustis obliquana	Throughout	Hawke's Bay: resistant to OP, cross-resistant to IGR-EA Bay of Plenty: resistant to P
	C. herana	Mainly South Island	No known resistance
Black lyre moth	Cnephasia jactatana	Throughout	No known resistance

¹ Insecticide types: OP = organophosphate, C = carbamate, IGR-BU = insect growth regulator - ecdysone antagonist, P = pyrethroid.

Current status of leafroller insecticide resistance in New Zealand

In New Zealand three species of leafroller have developed resistance to insecticides (Table 1). The lightbrown apple moth (Epiphyas postvittana) in Nelson and the greenheaded leafroller (Planotortrix octo) in Central Otago have developed resistance to organophosphate and carbamate insecticides. While in Hawke's Bay, P. octo and brownheaded leafroller (Ctenopseustis obliquana) have developed resistance to the OP azinphos-methyl. In addition, brownheaded leafroller in the Bay of Plenty had resistance to a pyrethroid insecticide. In all of these cases, the resistance problem extended over relatively few orchards.

Resistance to azinphos-methyl in both greenheaded and brownheaded leafrollers, gave cross-resistance to the IGR, Mimic. Exposing resistant P. octo to either insecticide increased the level of resistance to both products. Fortunately OP resistant populations of all three species remain susceptible to Match, an IGR from a different chemical group (Table 2).

Products with label claims for control of leafroller species in New Zealand

**Table 2:** Products with label claims for control of leafrollers in New Zealand (November 2002). Not all products listed for each pesticide may have a label claim for all crops indicated. X = label claim for leafroller control, C = label for caterpillar control, PB = pre-blossom.
	Type of label claim for each crop
Pesticide category and IRAC chemical group Pesticide common and (product) names
Carbamate 1A
carbaryl, (Carbaryl, Sevin)	X	X					X		X	X	X	X
methomyl (Lannate)		X			X		X
Organo-phosphate 1B
acephate (Lancer, Orthene)	X		X				C					C
acephate + fungicide (Saprene)							C
azinphos-methyl (No longer registered)		X	X		X	X				X	X
chlorpyriphos (Chlorpyriphos, Lorsban, Pychlorex, Spectrum)	X		X		X	X	C			X	X
diazinon (Basudin, Dew, Diazinon, Diazinyl, Gesapon)	X			X		X	C	X	X	X	X	X
dichlorvos (Nuvos)		C					C	C	C
parathion-methyl (No longer registered)	X	X	X	X	X	X		X	X	X	X	X
organo-phosphate + pyrethroid 1B/3
permethrin + diazinon (Averte)	X					X			X
permethrin + pirimiphos-methyl (Attack)	X		X		X	X	C		X
Pyrethroid 3
bifenthrin (Talstar)						PB
taufluvalinate (Mavrik)	X					X	C
taufluvalinate + fungicide (Guardall, Supershield)							C
Spinosyns 5
spinosad (Success Naturalyte)	X					X				X	X
Avemectin 6
abamectin (Apostle, Avid, Verdex)					X	X
Bta & Btk 11B1/11B2
Bt aizawai and Btk mixture (Agree WDG)						X
Btk 11B2
Bacillus thuringiensis kurstaki (Defin WG, Dipel DF, Dipel ES, MVP*II)	X	X	X		X	X
Benzyoyl-urea 15
lufenuron (Match)										X
Ecdysone agonist 18
tebufenozide (Mimic)	X				X	X				X	X
Oxadiazine 22
indoxacarb (Avaunt, Steward)						X				X

Warning: Some products listed may not be suitable for crops being exported to certain markets. Check with your export agency before applying any pesticide on export crops. Observe withholding periods.

Resistance management prevention strategy

Note: Control failure does not always imply resistance

The development of insecticide resistance by an insect is a rare event. For example, OP insecticides were used extensively against leafrollers in New Zealand for over 30 years before one population became resistant. Where leafroller control failure is experienced, first look for reasons other than resistance to explain the situation. For example, poor spray coverage through an incorrectly calibrated sprayer, use of incorrect product and water rates or applications timed against the wrong stage of the pest.

The general strategy is to reduce the potential for resistance by reducing populations of leafrollers within crops to very low levels and encouraging natural immigration of leafrollers that will mate with potentially resistant individuals. The offspring from the mating between susceptible and resistant moths will be more susceptible to the insecticide than the resistant parent. In fruit orchards, immigration of susceptible insects will occur naturally, especially in winter. Accurate spray timing, and careful targeting of applications should be used while selecting the insecticide from different chemical groups in a planned programme.

The above approach is best combined with management practices for the crop, shelter trees, and property, which aim to reduce leafroller numbers and improve insecticide coverage. Do not rely solely on chemicals for pest control. Wherever practicable, make use of cultural control measures such as crop hygiene and removal of weed hosts. Make maximum use of biological control wherever possible by choosing pesticides that are least harmful to natural enemies of pests and minimising the number of insecticide applications.

Insecticide use

Spray only when essential for control. Follow the guidelines and spray thresholds in integrated fruit production manuals, where available.
Comply with label rates.
Use insecticides from more than one chemical group (Table 2). Do not use multiple applications of one single product all season.
Use correct application procedures, observing correct tractor speeds and spraying conditions to obtain good insecticide coverage.
Calibrate sprayers at least once per season.
Follow spray programme recommendations, where they are available.
Use methods for monitoring leafrollers, where they are available (e.g. pheromone traps), to ensure effective spray timing. Learn the life cycle of orchard pests so that insecticides are used to their best advantage.
Confine sprays to the crop area: do not spray shelter or other areas around the orchard unless there is a clearly identified source of pest infestation.
If resistance is identified, it is essential to switch to another product with a different mode of action. Alternatively, use pheromone mating disruption to manage the situation. This tactic has worked well against resistant lightbrown apple moth and P. octo.

Crop management

Carry out adequate pruning and thinning where appropriate, to assist spray penetration and coverage, especially into fruiting clusters (e.g. pipfruit, grapes).
Maintain tree and plant sizes and shapes suitable for good spray coverage.
Control weeds, especially docks, plantains, blackberry, gorse, broom and clover, which are hosts of leafrollers.
Mow throughout the year to reduce leafroller populations in the ground cover.
Destroy mummified or old fruits during winter pruning, to prevent leafroller larvae using them as overwintering sites.

Shelter management

Use non-host shelter species such as Casuarina and bamboo. Avoid using shelter species that are favoured hosts, such as willows and poplars.
Remove nearby gorse, broom, blackberry and other host plants to reduce reservoirs of leafroller populations close to the crop.
Spray shelter only if absolutely essential, such as where shelter is known to be acting as a source of a crop infestation.

Implementation

This resistance management strategy should be included in industry-wide spray programmes for local and export horticultural crops.

Pesticides with label claims for leaf roller control should carry the following statement:

IMPORTANT - RESISTANCE MANAGEMENT
Resistance to this pesticide could develop from excessive use. To minimise this risk use strictly in accordance with label instructions. Avoid using this pesticide exclusively all season, and avoid unnecessary spraying. Maintain good cultural control practices.

References

Lo PL, Walker JTS, Suckling DM 2000. Insecticide resistance management of leafrollers (Lepidoptera: Tortricidae) in New Zealand. New Zealand Plant Protection 53: 163-167.

Suckling DM 1996. Leafroller resistance management strategy. In: Bourdot GW, Suckling DM ed. Pesticide Resistance: Prevention and Management. New Zealand Plant Protection Society, Lincoln, New Zealand. Pp 168-171.

Suckling DM, Khoo JGI, Rodgers DJ 1990. Resistance management of Epiphyas postvittana (Lepidoptera: Tortricidae) using mating disruption. New Zealand Journal of Crop & Horticultural Science 18: 89-98.

Wearing CH 1995. Mating disruption for management of organophosphate resistance in the greenheaded leafroller Planotortrix octo. Proceedings of the 48th NZ Plant Protection Conference: 46-51.

Wearing CH 1995. Resistance of Planotortrix octo to organophosphate insecticides in Dumbarton, Central Otago. Proceedings of the 48th NZ Plant Protection Conference: 40-45.